1. Field of the Invention
This invention generally relates to line card circuits for use with key telephone systems. More specifically, the subject invention concerns an improved K.T.U. line card circuit that is adapted to enable messages to be automatically transmitted from a key telephone station in response to an associated telephone at the station being operated to place a telephone line in a hold condition.
2. Description of the Prior Art
A typical key telephone is generally used to permit a subscriber to have several different telephone lines, i.e., each having a different number, available for use with a single telephone. Such key telephones thus may be recognized by the usual several line "buttons", or the like, that may be individually operated by a user to select a telephone line to be used from among several different telephone lines connected to the telephone. For example, a particular telephone line would be selected and used by depressing the corresponding button on the telephone and converting the telephone receiver to an off-hook condition.
As is well known, line card circuits are generally used in key telephone systems to control the operating condition of a telephone line and to control the operation of audible and visual signaling devices on the telephone. A single line card circuit is installed at a subscriber telephone station for each different telephone line servicing the telephone station.
A telephone line is generally capable of being in one of three operating conditions, i.e., a ringing condition, a seize condition, and a hold condition. The ringing condition would exist during periods in which ringing signals are being received at a key telephone of a subscriber being called. An audible signaling device such as a ringer, buzzer, or the like, that is situated at the key telephone being called, will ultimately respond to such ringing signals and provide an audible indication that an incoming telephone call is being received. A light positioned beneath, or in otherwise close proximity to the line button corresponding to a line on which an incoming call is being received will usually be illuminated to identify such telephone line at the key station. Such line button light would also be illuminated to identify the telephone line in use for outgoing telephone calls.
The seize condition exists during periods in which parties to a phone call have their respective telephones operated to permit a telephone conversation to be carried on.
The hold condition is generally used by a subscriber when it is desired to interrupt a telephone call without releasing the telephone line being used. For example, a subscriber may desire to answer an incoming call on a different telephone line, although the key telephone is already in use for a conversation on a different telephone line. The telephone line already in use would be placed in a hold condition by operation of a hold button to permit the incoming call to be answered with the same key telephone. The use of the original telephone can be later resumed by simply operating (usually by depression) the corresponding line button. Obviously, the hold condition permits several telephone lines to be served at once from a single key telephone.
When a telephone circuit is placed in a hold condition, a waiting party is presently left listening to either faintly heard beeping sounds or utter silence. In the event that no beeping sound is heard, a waiting party may be in doubt whether the telephone line connection has been somehow disconnected. In any case, holding a telephone receiver to an ear to hear beeping, or silence, for any extended length of time can be annoying as no doubt many telephone users will affirm.
It is accordingly the intention of the present invention to provide an improved line card circuit that permits a message such as a musical interlude, announcement, etc., to be automatically transmitted from a telephone station at which a key telephone has been operated to place a telephone line in a hold condition, such that waiting parties may be entertained by music or otherwise have the benefit of a recorded message, etc., and be relieved of any doubt that the telephone line in use has become disconnected.